1. Field of the Invention
This invention relates to capacitive proximity sensors for use in adverse engine environments such as, for example, the turbine section of a jet engine, and to proximity sensing and torque measurement systems incorporating such sensors.
2. Description of the Prior Art
There has previously been proposed a capacitive proximity sensor for operation under normal environmental conditions which detects the presence or absence of a liquid or solid in the immediate surrounds of the sensor. The electronic circuitry associated with the sensor is arranged adjacent thereto which avoids interference problems due to cabling between a sensor and remotely located associated circuitry.
Such a previously proposed arrangement is not, however, suitable for applications in hostile environments which demand a rugged sensor construction, a relative insensitivity of the sensor to environmental changes, remote location of the associated circuitry, and interference-free connection between the sensor and its associated circuitry. One typical such application is the measurement of the blade/shroud gap in the turbine section of a jet engine.
It has also been proposed to measure the torque transmitted by a shaft, for example a ships propeller shaft, by a magneto-strictive method. However, such a method is incompatible with the use of non-magnetic metals, is very sensitive to temperature variations, requires bulky equipment, and has low resolution.
It is therefore an object of the invention to provide an improved capacitive proximity sensor capable of operating in adverse environmental conditions. It is a further object of the invention to provide such a sensor for use in proximity sensing and torque measurement systems.